Wear leveling

ABSTRACT

In an example, a portion of a memory array may be selected to be wear leveled based on how often the portion is or is to be accessed. The portion may be wear leveled.

PRIORITY INFORMATION

This application is a continuation of U.S. application Ser. No.16/102,807, filed on Aug. 14, 2018, which is a continuation of U.S.application Ser. No. 15/669,290, filed Aug. 4, 2017, and issued as U.S.Pat. No. 10,198,195 on Feb. 5, 2019, the entire contents of which areincluded herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to electronic systems, such ascomputing systems and/or memory systems, and, more particularly, to wearleveling, such as in memory.

BACKGROUND

Memory is often implemented in electronic systems, such as computers,cell phones, hand-held devices, etc. There are many different types ofmemory, including volatile and non-volatile memory. Volatile memory mayrequire power to maintain its data and may include random-access memory(RAM), dynamic random-access memory (DRAM), static random-access memory(SRAM), and synchronous dynamic random-access memory (SDRAM).Non-volatile memory may provide persistent data by retaining stored datawhen not powered and may include NAND flash memory, NOR flash memory,nitride read only memory (NROM), phase-change memory (e.g., phase-changerandom access memory), resistive memory (e.g., resistive random-accessmemory), cross-point memory, ferroelectric-random-access memory (FeRAM),or the like. Hard disc drives (HDDs) may be an example of another typeof memory and may include magnetic tapes and/or optical discs.

The endurance of a memory may be defined as the number of writes, suchas the number of write/erase (e.g., program/erase) cycles, that thememory may endure before it can no longer reliably store data (e.g.,before it is likely to fail). For example, non-volatile memories mayhave lower endurance than DRAM.

In some examples, non-volatile memories may be divided into groups ofmemory cells, such as pages of memory cells, blocks of memory cells,etc. For example, some groups of memory cells may be subjected to highernumbers of writes than others and may be more likely to fail than groupssubjected to lower numbers of writes. For example, a memory may beconsidered to be likely to fail when one or more of its groups of memorycells has a high write/erase cycle count, while other groups might havea low write/erase cycle count.

In some examples, endurance may be improved by using wear leveling. Wearleveling may spread the writes across the groups of memory cells. Forexample, groups with higher write/erase cycle counts may be replacedwith groups with lower write/erase cycle counts during wear leveling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates an example of an apparatus inaccordance with a number of embodiments of the present disclosure.

FIG. 2 is a block diagram that illustrates another example of anapparatus in accordance with a number of embodiments of the presentdisclosure.

FIG. 3 is a block diagram that illustrates another example of anapparatus in accordance with a number of embodiments of the presentdisclosure.

FIG. 4 is a block diagram that illustrates another example of anapparatus in accordance with a number of embodiments of the presentdisclosure.

FIG. 5A illustrates an example of a memory array in accordance with anumber of embodiments of the present disclosure.

FIG. 5B illustrates an example of a memory cell in accordance with anumber of embodiments of the present disclosure.

DETAILED DESCRIPTION

In an example, a portion of a memory array may be selected to be wearleveled based on how often the portion is or is to be accessed. Theportion may be wear leveled.

A number of embodiments of the present disclosure provide benefits, suchas reduced bandwidth usage and/or reduced power consumption due to wearleveling compared to previous apparatus, such as memory systems.

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown, byway of illustration, specific examples. In the drawings, like numeralsdescribe substantially similar components throughout the several views.Other examples may be utilized and electrical changes may be madewithout departing from the scope of the present disclosure. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present disclosure is defined onlyby the appended claims and equivalents thereof.

In some existing memory, wear leveling may be applied to the entirememory array regardless of the usage of certain portions of the array.For example, wear leveling may be applied to portions of the memoryarray that might not need it, thereby consuming bandwidth and power.This problem may be exacerbated as memory densities increase.

A memory array may include a plurality of groups of memory cells, suchas pages of memory cells, blocks of memory cells, etc. In examples ofexisting wear-leveling schemes, such as round-robin schemes, a sparegroup of memory cells may replace an existing group, and the existinggroup may be made a spare group. For example, a logical addressassociated with the existing group may be remapped to the location ofthe spare group in the array in place of the location of the existinggroup in the array.

FIG. 1 is a block diagram of an apparatus, such as an electronic system100, in accordance with a number of embodiments of the presentdisclosure. Electronic system 100 may include a memory system, such as amemory 101 (e.g., an FeRAM), coupled to an apparatus (e.g., acontroller), such as a host 103 (e.g., a system on a chip (SOC)). Insome examples, host 103 may be a portion of a computing system, such asin a personal computer, a hand-held device, a cell phone, etc. Host 103may act as an interface between a processor, such as a centralprocessing unit (CPU), of the computing system and memory 101, forexample.

The term “coupled” may include electrically coupled, directly coupled,and/or directly connected with no intervening elements (e.g., by directphysical contact) or indirectly coupled and/or connected withintervening elements. The term coupled may further include two or moreelements that co-operate or interact with each other (e.g., as in acause and effect relationship).

Memory 101 may include a memory device 102 and a controller 104, such asa memory controller. Controller 104 might include a processor, forexample. Controller 104 may receive command signals (or commands),address signals (or addresses), and data signals (or data) from host 103over connections 105 and may output data to the host 103 overconnections 105.

Memory device 102 may include a memory array 106 of memory cells. Insome examples, memory array 106 may be divided into portions, such asbanks (e.g., partitions). Memory array 106 may include, for example, across-point memory array (e.g., a three-dimensional cross-point memoryarray), an array of ferroelectric memory cells, such as array 506 inFIG. 5A, a flash memory array (e.g., a NAND flash memory array), etc.

Memory device 102 may include address circuitry 108 to latch addresssignals provided over I/O connections 110 through I/O circuitry 112.Address signals may be received and decoded by a row decoder 114 and acolumn decoder 116 to access the memory array 106.

Memory device 102 may read data in memory array 106 by sensing voltageand/or current changes in the memory array columns using sense/buffercircuitry that in some examples may be read/latch circuitry 120.Read/latch circuitry 120 may read and latch data from the memory array106. I/O circuitry 112 may be included for bi-directional datacommunication over the I/O connections 110 with controller 104. Writecircuitry 122 may be included to write data to memory array 106.

Control circuitry 124 may decode signals provided by control connections126 from controller 104. These signals may include chip enable signals,write enable signals, and address latch signals that are used to controlthe operations on memory array 106, including data read, data write, anddata erase operations.

Control circuitry 124 may be included in controller 104, for example.Controller 104 may include, other circuitry, firmware, software, or thelike, whether alone or in combination. Controller 104 may be an externalcontroller (e.g., in a separate die from the memory array 106, whetherwholly or in part) or an internal controller (e.g., included in a samedie as the memory array 106). For example, an internal controller mightbe a state machine or a memory sequencer. In some examples, wherecontroller 104 might be an internal controller, controller 104 might bepart of memory device 102.

Controller 104 may include one or more registers 130 (e.g., latches). Insome examples, a state of (e.g., a value in) a register 130 may indicatewhether a corresponding portion of array 106 is selected to be wearleveled and is thus to be wear leveled in response to a wear-levelingcommand received over connections 105 at controller 104 from host 103.For example, the state of a register 130 (e.g., either logical high orlogical low) may be set, in response to a wear-leveling set-up commandreceived over connections 105 at controller 104 from host 103, toindicate whether a corresponding portion of array 106 is selected forwear leveling and is thus to be wear leveled in response to awear-leveling command from host 103. In other examples, a register 130may store an address of a last accessed (written, read, and/or erased)portion of array 106. For example, the last accessed portion (e.g., onlythe last accessed portion) of array 106 may be selected for wearleveling and thus may be wear leveled in response to a wear levelingcommand.

In some examples, host 103 may keep track of the number of times eachportion of array 106 is accessed. For example, host 103 may keep trackof the number of times each portion of array 106 is written to or thenumber of write/erase cycles that are performed on each portion of array106. Host 103 may include one or more counters 135 to count of the ofthe number of times a portion of array 106 is accessed, such as thenumber of times the portion is written to or the number of times awrite/erase cycle is performed on the portion (e.g., the number ofwrite/erase cycles). For example, there may be a counter 135 for eachportion of array 106. The count of a counter 135 may be reset (e.g., tozero) at power up of system 100, for example.

In some examples, refresh signals (e.g., refresh commands), such as thetype that may be commonly used for DRAM, may be provided by connections105. For example, a refresh command might be used instead of awear-leveling command to initiate (e.g., trigger) wear leveling. Duringa typical DRAM refresh, for example, data may be read from a memorylocation, and the read data may be written back to that memory location.

In some examples, controller 104 may include an address converter, suchas an address conversion table 137. For example, address conversiontable 137 may convert logical addresses received from host 103 tolocations (e.g., physical addresses of locations) of groups of memorycells within memory array 106. In some examples, there may be adedicated address conversion table 137 for each portion of memory array106 that may convert logical addresses, corresponding to that portion,from host 103 to physical addresses for that portion.

FIG. 2 is a block diagram of an example of an apparatus, such as anelectronic system 200 that may be a portion of electronic system 100 inaccordance with a number of embodiments of the present disclosure. Forexample, electronic system 200 may include a memory 201, that may be aportion of memory 101, coupled to a host 203 that may be a portion ofhost 103. For example, memory 201 may include a controller, such ascontroller 104, coupled to a memory device, such as memory device 102.In some examples, the controller of memory 201 might be part of thememory device of memory 201 (e.g., and memory 201 might be referred toas a memory device).

Memory 201 may include a memory array 206 that may be a portion ofmemory array 106 and that may be divided into a plurality of portions240, such as banks (e.g., partitions). For example, memory array 206 mayinclude portions 240-1 to 240-4. However, the number of portions 240might not be limited to four portions. Each portion 240 may be addressedindividually and may be accessed individually. For example, each portion240 may be written, read, and/or erased individually. In some examples,a read command and a write command may include an address of aparticular one of portions 240-1 to 240-4. Moreover, each portion 240may be wear leveled individually and independently of the other portions240. Each portion 240 may, for example, include a plurality of groups ofmemory cells, such as pages of memory cells, blocks of memory cells,etc.

Memory 201 may include registers 230-1 to 230-4, such as mode registers,(e.g., latches) that may be a portion of the register 130 in FIG. 1 inaccordance with a number of embodiments of the present disclosure.Respective ones of registers 230-1 to 230-4 may respectively correspondto corresponding ones of portions 240-1 to 240-4.

Counters 235-1 to 235-4 may be a portion of the counter 135 in FIG. 1 inaccordance with a number of embodiments of the present disclosure.However, the number of counters might not be limited to four. In someexamples, respective ones of counters 235-1 to 235-4 of host 203 mayrespectively correspond to corresponding ones of portions 240-1 to240-4. A counter 235 may count the number of times a corresponding oneof portions 240-1 to 240-4 is accessed. For example, a signal 241 may besent to a counter 235 that may increment the count each time thecorresponding portion 240 is accessed. For example, the count mayindicate the number of times the corresponding portion 240 has beenaccessed.

Wear-leveling may be performed on certain selected ones of portions240-1 to 240-4 in response to a command 242 that may be a wear-levelingcommand or a refresh command from host 203. In some examples, the stateof a register 230 may indicate whether the corresponding one of portions240 is to be wear-leveled in response to a command 242. For example, alogical high, such as a logical one (1), may be stored in a register 230to select a corresponding one of portions 240 to be wear-leveled inresponse to a command 242, and a logical low, such as a logical zero(0), may be stored in a register 230 whose corresponding portion 240 isto be ignored (e.g., is not selected to be wear leveled) in response toa command 242. Although a logical high in a register 230 may be used toindicate that the corresponding portion 240 is to be wear leveled (e.g.,to select the corresponding portion 240 to be wear leveled), and alogical low in a register 230 may be used to indicate that thecorresponding portion 240 is not to be wear leveled (e.g., to not selectthe corresponding portion 240 to be wear leveled), in other examples,the roles of logical high and logical low may be reversed.

In some examples, host 203 may know in advance which of the portions 240might be accessed most frequently. For example, the portions 240 thatmay be accessed most frequently may be wear leveled in response to acommand 242, whereas those portions that may be accessed relativelyinfrequently may not be wear leveled in response to a command 242 Forexample, the portions 240 that may be accessed most frequently may beselected to be wear leveled, whereas those portions that may be accessedrelatively infrequently may not be selected to be wear leveled.

In some examples, host 203 may send a setup command 244 to memory 201that may indicate to memory 201 which registers 230 are to be set to astate (e.g., a logical high) that indicates wear leveling is to beperformed on the corresponding portions 240 based on how often thosecorresponding portions 240 are to be accessed and which registers 230are to be set to a state (e.g., a logical low) that indicates wearleveling is not to be performed on the corresponding portions 240 basedon how often those corresponding portions 240 are to be accessed. Theregisters 230 may be set in response to this command. For example,respective ones of registers 230-1 to 230-4 may respectively indicatewhether corresponding ones of portions 240-1 to 240-4 are (e.g., whethercorresponding ones of portions 240-1 to 240-4 are selected) to be wearleveled based on how often the corresponding ones of portions 240-1 to240-4 are to be respectively accessed. In some examples, a register 230may be set to indicate that the corresponding portion 240 is to be wearleveled in response to the number (e.g., expected number) of accesses tobe performed being greater than or equal to a certain number.

A setup command 244 may be sent to memory 201 each time system 200 ispowered up (e.g., once per power up), for example. In some examples,host 203 may write a state to a register 230 based on whether wearleveling is to be performed on the corresponding portion 240.

In some examples, a logical low in a register 230 may act to prevent(e.g., lock out) the corresponding portion 240 from being wear leveledso that only portions 240 corresponding to registers 230 having alogical high may be (e.g., selected to be) wear leveled in response tocommand 242. In the example of FIG. 2, the logical zeros in registers230-1 and 230-3 may act to respectively prevent portions 240-1 and 240-3from being wear leveled in response to command 242 so that only portions240-2 and 240-4 respectively corresponding to registers 230-2 and 230-4having logical ones may be wear leveled in response to command 242. Forexample, only portions 240-2 and 240-4 may be selected to be wearleveled.

Host 203 may monitor the counts on counters 235. When a count of acounter 235 is greater than or equal to a certain value (e.g.,representing a certain number of accesses to the corresponding portion240), host 203 may set the corresponding register 230 to a logical high,such as by writing a logical one in the corresponding register 230 or bysending a setup command 244 that causes memory 201 to store a logicalone in the corresponding register 230. For the example of FIG. 2, inresponse to the count on counter 235-1 becoming greater than or equal tothe certain value, host 203 may cause the value in the correspondingregister 230-1 to be changed to a logical one from a logical zero (e.g.,by sending a setup command 244 to memory 201 that may cause the value tobe changed or by writing the logical one in register 230-1)

In some examples, host 203 may determine the number of accesses per unittime (e.g. the rate of accesses) for each portion 240 from the count ofthe corresponding counter 235. For example, host 203 may set a register230 to a logical low or high based on the rate of accesses to thecorresponding portion 240. For the example of FIG. 2, in response to therate of accesses to portion 240-1 becoming greater than or equal to acertain value, host 203 may change the value in the correspondingregister 230-1 to a logical one from a logical zero, and in response tothe rate of accesses to portion 240-2 being less than the certain value,host 203 may change the value in the corresponding register 230-2 to alogical zero from a logical one.

FIG. 3 is a block diagram of an example of an apparatus, such as anelectronic system 300 that may be a portion of electronic system 100 inaccordance with a number of embodiments of the present disclosure. Forexample, electronic system 300 may include a memory 301, that may be aportion of memory 101, coupled to a host 303 that may be a portion ofhost 103. For example, memory 301 may include a controller, such ascontroller 104, coupled to a memory device, such as memory device 102.In some examples, the controller of memory 301 might be part of thememory device of memory 301 (e.g., and memory 301 might be referred toas a memory device).

Memory 301 may include a memory array 306 that may be a portion ofmemory array 106 and that may be divided into a plurality of portions340, such as banks (e.g., partitions). For example, memory array 306 mayinclude portions 340-1 to 340-4. However, the number of portions 340might not be limited to four portions. Each portion 340 may be addressedindividually and may be accessed individually. For example, each portion340 may be written, read, and/or erased individually. In some examples,a read command and a write command may include an address of aparticular one of portions 340-1 to 340-4. Moreover, each portion 340may be wear leveled individually and independently of the other portions340. Each portion 340 may, for example, include a plurality of groups ofmemory cells, such as pages of memory cells, blocks of memory cells,etc.

Counters 335-1 to 335-4 may be a portion of the counter 135 in FIG. 1 inaccordance with a number of embodiments of the present disclosure.However, the number of counters might not be limited to four. In someexamples, respective ones of counters 335-1 to 335-4 of host 303 mayrespectively correspond to corresponding ones of portions 340-1 to340-4. A counter 335 may count the number of times a corresponding oneof portions 340-1 to 340-4 is accessed. For example, a signal 341 may besent to a counter 335 that may increment the count each time thecorresponding portion 340 is accessed. For example, the count mayindicate the number of times the corresponding portion 340 has beenaccessed.

A command 342, such as a wear-leveling command or a refresh command, maybe sent from host 303 to memory 301 to cause (e.g., to select) portions340 to be wear leveled. For example, command 342 may contain theaddresses of particular portions 340 (e.g., selected) to be wearleveled. As such, command 342 may be referred to as a portion-directedcommand, for example. In some examples, command 343 may includeaddresses for less than all of the portions 340. For example, command342 may include the addresses of the portions 340 that may be accessedmost frequently. Note that only the portions 340 whose addresses are incommand 342 may be wear leveled, for example. For example, only theportions 340 whose addresses are in command 342 are selected for wearleveling

In some examples, host 303 may know in advance which of the portions 340might be accessed most frequently, and may include the addresses ofthose portions in command 342. For example, an address may be includedbased on how often the portion having that address is (e.g., expected)to be accessed. In other examples, the addresses in command 342 mayinclude addresses of portions that are to be excluded from wear levelingbased on how often those portions are (e.g., expected) to be accessed,where those portions whose addresses do not appear are wear leveled inresponse to command 342. For example, the command may indicate directlyonly those portions that are to be wear leveled by expressly includingonly the addresses of those portions or may indicate indirectly onlythose portions that are to be wear leveled by including the addresses ofonly portions that are not to be wear leveled such that only theexcluded addresses are to be wear leveled. In this way, for example, thecommand may directly or indirectly select only those portions that areto be wear leveled.

In other examples, host 303 may monitor the counts on counters 335. Inresponse to a count of a counter 335 becoming greater than or equal to acertain value (e.g., representing a certain number of accesses to thecorresponding portion 340), host 303 may add the address of thecorresponding portion 340 to command 342.

In some examples, host 303 may determine the number of accesses per unittime (e.g. the rate of accesses) for each portion 340 from the count ofthe corresponding counter 335. For example, in response to a rate ofaccesses to a portion 340 becoming greater than or equal to a certainvalue, host 303 may add the address of that portion 340 to command 342,and in response to a rate of accesses to a portion 340 becoming lessthan the certain value, host 303 may remove the address of that portion340 from command 342.

FIG. 4 is a block diagram of an example of an apparatus, such as anelectronic system 400 that may be a portion of electronic system 100 inaccordance with a number of embodiments of the present disclosure. Forexample, electronic system 400 may include a memory 401, that may be aportion of memory 101, coupled to a host 403 that may be a portion ofhost 103. For example, memory 401 may include a controller, such ascontroller 104, coupled to a memory device, such as memory device 102.In some examples, the controller of memory 401 might be part of thememory device of memory 401 (e.g., and memory 401 might be referred toas a memory device).

Memory 401 may include a memory array 406 that may be a portion ofmemory array 106 and that may be divided into a plurality of portions440, such as banks (e.g., partitions). For example, memory array 406 mayinclude portions 440-1 to 440-4. However, the number of portions 440might not be limited to four portions. Each portion 440 may be addressedindividually and may be accessed individually. For example, each portion440 may be written, read, and/or erased individually. In some examples,a read command and a write command may include an address of aparticular one of portions 440-1 to 440-4. Moreover, each portion 440may be wear leveled individually and independently of the other portions440. Each portion 440 may, for example, include a plurality of groups ofmemory cells, such as pages of memory cells, blocks of memory cells,etc.

Host 403 may send a command 442, such as a wear-leveling command or arefresh command to memory 401. Memory 401 may include a register 430(e.g., a latch) that may, for example, be a portion of the register 130in FIG. 1 in accordance with a number of embodiments of the presentdisclosure. Register 430 may store the address of the last accessedportion 440 of the portions 440 (e.g., portions 440-1 to 440-4). Memory401 may wear level the portion 440 whose address is in register 430 inresponse to receiving the next command 442 after the address is storedin register 430. For example, memory 401 may read the address inregister 430 in response to command 442 and may wear level the portion440 having that address. For example, the address of the last accessedportion 440 being in register 430 may select that portion for wearleveling.

It is expected, for example, that the number of times the address of aparticular last accessed portion 440 appears in register 430 (e.g., thefrequency at which the address of the particular last accessed portion440 appears in register 430) is a measure (e.g., at least statistically)of how often that particular portion 440 is accessed. For example, thoseportions 440 whose addresses appear most often in register 430 are mostlikely to have been accessed most often, and those portions 440 whoseaddresses appear least often in register 430 are most likely to havebeen accessed least often. For example, selecting a portion 440 whoseaddress is in register 430 may be analogous to selecting that portion440 based on the number of accesses to that portion 440 being greaterthat the remaining portions 440. For example, selecting a portion 440whose address is in register 430 may be analogous to selecting thatportion based on how often that portion is or is to be accessed.

In some examples, the wear leveling discussed above may be performed asbackground operations, such as while read or write operations are beingperformed. The wear leveling to be performed on a portion of a memoryarray in response to a command from a host, for example, may bepostponed if higher-priority (e.g., latency-critical) operations, suchas some reads or writes, might need to be performed.

In some examples, each portion of a memory array, such as each portion240 in FIG. 2, each portion 340 in FIG. 3, and each portion 440 in FIG.4, may have its own exclusive (e.g., exclusive to all other groups) setof groups of in-use blocks and its own exclusive set of spare blocks,for example. In some examples, wear leveling in a (e.g., in each)portion of a memory array may include replacing a group of memory cellsthat is in use, such as an existing group, with a replacement sparegroup of memory cells. For example, a logical address that may be mappedto the location (e.g., physical address) of the existing group in aportion of a memory array may be remapped to the location of thereplacement spare group in that portion. The logical addresscorresponding to the existing group may be remapped to address of thereplacement spare group, for example, by changing the physical addressof the existing group in an address conversion table, such as addressconversion table 137, for the portion of the memory array to thephysical address of the replacement spare group in that portion. Forexample, as indicated above in conjunction with FIG. 1, there may be adedicated address conversion table 137 for each portion of memory array106, such as each portion 240, 340, and 440.

The wear leveling in a portion (e.g., each portion) of a memory arraymay include, for example, a round-robin operation, where a spare groupin a first position in a queue of spare groups (e.g., exclusively forthat portion) may replace the existing group and the existing group maybe placed in the last position in the queue of spare groups. Insubsequent wear leveling operations, starting from the last position inthe queue, a spare group may move until it reaches the first position inthe queue and eventually replaces an existing block. For example, duringeach wear leveling, a spare group in the last position may be displacedtoward the first position by an existing block that has been replaced.

FIG. 5A illustrates an example of a memory array 506, such as aferroelectric memory array, in accordance with a number of embodimentsof the present disclosure. For example, memory array 506 may be a memoryarray 106, 206, 306, and/or 406.

Memory array 506 may include memory cells 508 that may be programmableto store different states. A memory cell 508 may include a capacitor tostore a charge representative of the programmable states. For example, acharged and uncharged capacitor may respectively represent two logicstates. Memory cell 508 may include a capacitor with a ferroelectricmaterial, in some examples. For example, ferroelectric materials mayhave a spontaneous electric polarization (e.g., they may have a non-zeropolarization in the absence of an electric field. Different levels ofcharge of a ferroelectric capacitor may represent different logicstates, for example.

A memory cell 508 may be coupled to a respective access line, such as arespective one of access lines 510-1 to 510-M, and a respective data(e.g., digit) line, such as one of data lines 515-1 to 515-N. Forexample, a memory cell 508 may be coupled between an access line 510 anda data line 515. In some examples, access lines 510 may also be referredto as word lines, and data lines 515 may also be referred to as bitlines. Access lines 510 and data lines 515, for example, may be made ofconductive materials, such as copper, aluminum, gold, tungsten, etc.,metal alloys, other conductive materials, or the like.

In some examples, memory cells 508 commonly coupled to an access line510 may be referred to as a row of memory cells. For example, accesslines 510 may be coupled to row decoder 114, and data lines may becoupled to column decoder 116. Operations such as reading and writingmay be performed on memory cells 508 by activating or selecting theappropriate access line 510 and a data line 515 (e.g., by applying avoltage to the access line). Activating an access line 510 mayelectrically couple the corresponding row of memory cells 508 to theirrespective data lines 515.

FIG. 5B illustrates an example circuit 520 that includes a memory cell508 in accordance with a number of embodiments of the presentdisclosure. Circuit 520 may include a ferroelectric memory cell 508A, anaccess line 510A, and a data line 515A that may respectively be examplesof a memory cell 508, an access line 510, and a data line 515, shown inFIG. 5A.

Memory cell 508A may include a logic storage component, such ascapacitor 525 that may have a first plate, such as a cell plate 530, anda second plate, such as a cell bottom 535. Cell plate 530 and cellbottom 535 may be capacitively coupled through a ferroelectric material540 positioned between them. The orientation of cell plate 530 and cellbottom 535 may be flipped without changing the operation of memory cell508A.

Circuit 520 may include a select device 550, such as a selecttransistor. For example, the control gate 552 of select device 550 maybe coupled to access line 510A. In the example of FIG. 5B, cell plate530 may be accessed via plate line 555, and cell bottom 535 may beaccessed via data line 515A. For example, select device 550 may be toselectively couple data line 515A to cell bottom 535 in response toaccess line 510A activating select device 550. For example, capacitor525 may be electrically isolated from data line 515A when select device550 is deactivated, and capacitor 525 may be electrically coupled todata line 515A when select device 550 is activated. Activating selectdevice 550 may be referred to as selecting memory cell 508A, forexample. As previously described, various states may be stored bycharging or discharging capacitor 525.

Although specific examples have been illustrated and described herein,those of ordinary skill in the art will appreciate that an arrangementcalculated to achieve the same results can be substituted for thespecific embodiments shown. This disclosure is intended to coveradaptations or variations of one or more embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. The scope ofone or more examples of the present disclosure should be determined withreference to the appended claims, along with the full range ofequivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus, comprising: an array of memorycells comprising a first portion and a second portion; and a controllercomprising: a first register corresponding to the first portion; and asecond register corresponding to the second portion; the controllerconfigured to, in response to a command from a host, set the secondregister to a first state to indicate that the second portion isselected to be wear leveled, while the first portion is also selected tobe wear leveled, based on how often the second portion is or is to beaccessed.
 2. The apparatus of claim 1, wherein the controller comprisesa plurality of address conversion tables dedicated for each of the firstportion and the second portion of the array of memory cells.
 3. Theapparatus of claim 1, wherein the command received from the hostcomprises addresses of each of a plurality of portions of the array ofmemory cells except for addresses of the first and the second portions.4. The apparatus of claim 1, wherein the command received from the hostcomprises addresses of the first and the second portions.
 5. Theapparatus of claim 1, wherein the command is a wear-leveling command ora refresh command.
 6. A method, comprising: selecting, to wear level afirst portion of an array of memory cells, the first portion by settinga first register corresponding to the first portion based on how oftenthe first portion is or is to be accessed; and while the first portionis selected, selecting, to wear level a second portion of they array,the second portion by setting a second register corresponding to thesecond portion based on how often the second portion is or is to beaccessed.
 7. The method of claim 6, further comprising selecting thefirst portion in response to the first portion being accessed greaterthan or equal to a certain number of times.
 8. The method of claim 6,further comprising selectin the first portion in response to a rate ofaccesses to the first portion being greater than a threshold.
 9. Themethod of claim 6, wherein selecting the first portion and the secondportion comprises selecting a portion of the array having an addressspecified in a command received from a host.
 10. The method of claim 6,wherein the array of memory cells comprise a plurality of portionscomprising the first portion and the second portion, and the methodfurther comprises not allowing a remaining portion of the plurality ofportions to be wear leveled.
 11. The method of claim 6, whereinselecting the first portion and the second portion comprises selecting aportion of the array whose address is not specified in a commandreceived from a host.
 12. The method of claim 6, further comprising wearleveling the first portion and the second portion independently of eachother.
 13. The method of claim 6, further comprising setting the firstportion and the second portion in response to a command from a host. 14.A system, comprising: a memory comprising: a first registercorresponding to a first portion of an array of memory cells; a secondregister corresponding to a second portion of an array of memory cells;a host coupled to the memory, the host configured to: allow the firstportion to be wear leveled by setting the first register; and preventthe second portion from being wear leveled by setting the secondregister.
 15. The system of claim 14, wherein: the host comprises: afirst counter corresponding to the first portion; and a second countercorresponding to the second portion; and the host is configured tomonitor how often each of the first portion and the second portion isaccessed based on a count of the first counter and the second counter.16. The system of claim 15, wherein the host is configured to: send, tothe memory, a setup command in response to determining that a count ofthe first register is greater than or equal to a threshold; and thefirst register is configured to be, in response to the setup command,set to a first state to indicate that the first portion is selected tobe wear leveled.
 17. The system of claim 15, wherein the host isconfigured to prevent the second portion from being wear leveled inresponse to a count of the second count being less than a threshold. 18.The system of claim 15, wherein a count of each of the first counter andthe second counter indicates at least one of: a number of times arespective one of the first portion and the second portion is accessed;and a rate of accesses to a respective one of the first portion and thesecond portion.
 19. The system of claim 15, wherein a count of each ofthe first counter and the second counter indicates a number of times arespective one of the first portion and the second portion is expectedto be accessed.
 20. The system of claim 15, wherein the host isconfigured to send the setup command each time the system is powered up.